863 research outputs found
Thrust chamber material technology program
This report covers work performed at Pratt & Whitney on development of copper-based materials for long-life, reusable, regeneratively cooled rocket engine thrust chambers. The program approached the goal of enhanced cyclic life through the application of rapid solidification to alloy development, to introduce fine dispersions to strengthen and stabilize the alloys at elevated temperatures. After screening of alloy systems, copper-based alloys containing Cr, Co, Hf, Ag, Ti, and Zr were processed by rapid-solidification atomization in bulk quantities. Those bulk alloys showing the most promise were characterized by tensile testing, thermal conductivity testing, and elevated-temperature, low-cycle fatigue (LFC) testing. Characterization indicated that Cu- 1.1 percent Hf exhibited the greatest potential as an improved-life thrust chamber material, exhibiting LCF life about four times that of NASA-Z. Other alloys (Cu- 0.6 percent Zr, and Cu- 0.6 percent Zr- 1.0 percent Cr) exhibited promise for use in this application, but needed more development work to balance properties
Digital image registration method based upon binary boundary maps
A relatively fast method is presented for matching or registering the digital data of imagery from the same ground scene acquired at different times, or from different multispectral images, sensors, or both. It is assumed that the digital images can be registed by using translations and rotations only, that the images are of the same scale, and that little or no distortion exists between images. It is further assumed that by working with several local areas of the image, the rotational effects in the local areas can be neglected. Thus, by treating the misalignments of local areas as translations, it is possible to determine rotational and translational misalignments for a larger portion of the image containing the local areas. This procedure of determining the misalignment and then registering the data according to the misalignment can be repeated until the desired degree of registration is achieved. The method to be presented is based upon the use of binary boundary maps produced from the raw digital imagery rather than the raw digital data
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Cross-platform validation of notional baseline architecture models of naval electric ship power systems
To support efforts in assessing the relative merit of alternative power system architectures for future naval combatants, the Electric Ship Research and Development Consortium (ESRDC) has developed notional baseline models for each of the primary candidate architectures currently considered, medium-voltage DC (MVDC), conventional 60 Hz medium-voltage (MVAC), and high-frequency medium-voltage (HFAC). Initial efforts have focused on the development of a consistent set of component models, of which the system models can be comprised, and the basic definition of the system models. The broader objectives of the consortium, however, go beyond the definition of the baseline models. The focus is on the process by which the models are implemented in software and validated, the process by which the performance of the disparate system models are objectively and quantitatively assessed and compared, and, ultimately, the process by which the relative merits of the architectures may be assessed. This paper focuses specifically on cross-platform component validation.Center for Electromechanic
Generalized and multi-oscillation solitons in the Nonlinear Schr\"odinger Equation with quartic dispersion
We study different types of solitons of a generalized nonlinear Schr\"odinger
equation (GNLSE) that models optical pulses traveling down an optical waveguide
with quadratic as well as quartic dispersion. A traveling-wave ansatz
transforms this partial differential equation into a fourth-order nonlinear
ordinary differential equation (ODE) that is Hamiltonian and has two reversible
symmetries. Homoclinic orbits of the ODE that connect the origin to itself
represent solitons of the GNLSE, and this allows us to study the existence and
organization of solitons with advanced numerical tools for the detection and
continuation of connecting orbits. In this way, we establish the existence of
connections from one periodic orbit to another, called PtoP connections. They
give rise to families of homoclinic orbits to either of the two periodic
orbits; in the GNLSE they correspond to generalized solitons with oscillating
tails whose amplitude does not decay but reaches a nonzero limit. Moreover,
PtoP connections can be found in the energy level of the origin, where
connections between this equilibrium and a given periodic orbit, called EtoP
connections, are known to organize families of solitons. As we show here, EtoP
and PtoP cycles can be assembled into different types of heteroclinic cycles
that give rise to additional families of homoclinic orbits to the origin. In
the GNLSE, these correspond to multi-oscillation solitons that feature several
episodes of different oscillations in between their decaying tails. As for
solitons organized by EtoP connections only, multi-oscillation solitons are
shown to be an integral part of the phenomenon of truncated homoclinic snaking.Comment: 25 Pages, 13 figure
The Impact of an International Interprofessional Experience on Perceptions of Pharmacist-Physician Relationships
Objective. To assess the impact of this international interprofessional learning experience on perceptions of pharmacist-physician relationships and interprofessional teams.
Methods. Medical and pharmacy students completed a one-week interprofessional medical mission experience in the Dominican Republic. Anonymous surveys were administered to 17 students before and after completion to measure perceptions of pharmacist-physician relationships and interprofessional teams. Responses were matched and changes in perceptions were analyzed using the Wilcoxon Signed Rank test. The SPICE-R2 instrument was administered after the experience to measure attitudes toward interprofessional teams.
Results. Of the 17 participants, 100% responded to all surveys. Significant improvements were seen in the perception of pharmacists as an integral part of medical mission trips (P=0.035) and confidence in the ability to communicate with other healthcare disciplines (P=0.033). All students stated they would recommend this experience, and agreed that interprofessional experiences enhance their team work skills and should be incorporated into their education. Student comments supported that this was a meaningful and effective interprofessional experience. The results of the SPICE-R2 demonstrated positive attitudes about interprofessional teams, with all questions having a median score of “agree” or “strongly agree.”
Conclusions. An international interprofessional experience improved the perception of pharmacist-physician relationships. The experience provided understanding of the other healthcare discipline, an appreciation for the importance of interprofessional teamwork, increased student confidence in communicating with the other discipline, and cultivated interest in future interprofessional collaboration
Complex switching dynamics of interacting light in a ring resonator
Microresonators are micron-scale optical systems that confine light using
total internal reflection. These optical systems have gained interest in the
last two decades due to their compact sizes, unprecedented measurement
capabilities, and widespread applications. The increasingly high finesse (or
factor) of such resonators means that nonlinear effects are unavoidable
even for low power, making them attractive for nonlinear applications,
including optical comb generation and second harmonic generation. In addition,
light in these nonlinear resonators may exhibit chaotic behavior across wide
parameter regions. Hence, it is necessary to understand how, where, and what
types of such chaotic dynamics occur before they can be used in practical
devices. We consider a pair of coupled differential equations that describes
the interactions of two optical beams in a single-mode resonator with symmetric
pumping. Recently, it was shown that this system exhibits a wide range of
fascinating behaviors, including bistability, symmetry breaking, chaos, and
self-switching oscillations. We employ here a dynamical system approach to
identify, delimit, and explain the regions where such different behaviors can
be observed. Specifically, we find that different kinds of self-switching
oscillations are created via the collision of a pair of asymmetric periodic
orbits or chaotic attractors at Shilnikov homoclinic bifurcations, which acts
as a gluing bifurcation. We present a bifurcation diagram that shows how these
global bifurcations are organized by a Belyakov transition point (where the
stability of the homoclinic orbit changes). In this way, we map out distinct
transitions to different chaotic switching behavior that should be expected
from this optical device.Comment: 22 pages, 10 figure
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